In recent years an automated sorting of domestic waste, sorted at source, into different fractions has become more and more important in order to increase the efficiency of the waste handling facilities and in order to be able to take care of the ever growing amounts of waste produced by the households.
There are a number of different methods and systems available today to perform this type of sorting. WO95/32062 discloses an arrangement for sorting differently coloured waste sacks which occur in random distributions and contain different types of waste sorted at source. This arrangement comprises sorting stations, which by means of a colour analysis as disclosed in WO9622512 identify and then separate waste sacks of a predetermined color, which are conveyed on a conveyor belt.
In EP 1 583 618 the refuse sacks are provided with a means of identification, in this case the entire bag is provided with a specific colour, and the sorting is performed at least one sorting station, which is able to identify at least two means of identification, this method and arrangement thus further enhances the accuracy of the sorting.
As the amounts of domestic waste continues to increase there is a need for efficient sorting, and also a sorting that can take into account the wish that it should be possible to make use of the different fractions of the waste, for instance in biogas production of organic waste. The demands for specificity in the sorting for this type of waste are high, as plastics and other unwanted materials can clog the production of biogas and even in a worst case scenario render the entire biogas facility unuseable.
Sorting waste in bags having different colours is advantageous in that it is pedagogic, i.e. the user can easily decide which bag to use for a particular type of waste, and that all the waste bags may be placed in one and the same waste container, which makes it easy when the waste is to be collected. One problem with having coloured bags is however that waste sorting can be tedious and if the bag is coloured the user may experience a sense that it doesn't matter if he puts something in the wrong bag, or if he does not sort the waste at all. There is thus a need for a solution in which the user can easily see what the bag is supposed to contain and the personnel at the waste handling facility may visually inspect to see that nothing has been wrongfully placed in the bag. One way of solving this problem is to make a transparent bag. It must however still be possible for the user to determine what type of waste he bag is meant to be filled and to sort the bag in a convenient and most of all accurate manner at the waste handling facility.